2.4 mm trouble [possible lru race]

Quoted 11 lines · Roman Zippel

Hi,

Quoted 6 lines · Richard Zidlicky

First I suspected a stale TLB entry so I've added pretty many extra flushes througout the code. This does very much reduce the risk of the problem, but the problem still happens if swapping is increased so it might very well be something else.

Any ideas?

Quoted 5 lines

It sounds like a cache problem. I had to fix one early 2.4, so maybe there is another one.
It would help a lot if you could reproduce it within gdb to get some more information about the context of the crash (e.g. invalid data or code, the type of mapping (from /proc/<pid>/maps)).

hm, I am now testing the appended patch, which is a backport to 2.4.19 of this:

From: Daniel Phillips <[email protected]>
To: Marcelo Tosatti <[email protected]>,
"Christian Ehrhardt" <[email protected]>
Subject: [CFT] [PATCH] LRU race fix
Date: Tue, 17 Sep 2002 19:03:19 +0200
X-Mailer: KMail [version 1.3.2]
Cc: <[email protected]>

This patch against 2.4.20-pre7 fixes a theoretical race where a page could possibly be freed while still on the lru list. The details have been discussed at length earlier, see "[RFC] [PATCH] Include LRU in page count".

The race may not even be that theoretical, it's just so rare that when it does happen, it might be dismissed as a driver problem or similar...

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Somehow this does completely fix my problem, I have taken out all the tlb related hacks and the testcase that caused the problem 100% now runs without any sign of problems :))

Now I am wondering if that is just coincidence or why m68k hit that error so reliably.. is it supposed to have any effect at all on UP?